Flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. Once data have been written into the flash memory, they will be kept for a period of time even if the electric power is removed. A flash memory device has advantages of: small size, large storage volume, fast read/write speed, less power consumption, quiet and less prone to mechanical failure. It is widely used in embedded systems, portable information devices and consumer electronics.
Since flash memory device has the aforementioned advantages, data storage devices for temporarily data storing on the market, such as memory cards and USB drives, are all flash memory devices. Furthermore, some data storage devices for long-term data storing, such as hard disk drives, are also flash memory devices (solid state disk, SSD).
However, flash memory cells have a limited number of write and erase cycles, limited period of data retention, read disturb and write disturb.
The period of data retention is closely related to program/erase (P/E) cycles. The period of data retention will be shortened greatly after the P/E cycles exceed a predetermined number. Once data have been stored in a flash memory device longer than the period of data retention of the flash memory device, even if there is no read or write process been performed, bit error may occur.
Consequently, how to extend the period of data retention of a flash memory to prevent the data stored in the flash memory from error is the problem of the community.